Since the demonstration in 1987 that the small open reading frame within HIV-1 designated R encodes a 15 kd protein (Wong-Staal, F., et al., (1987) AIDS Res. Hum. Retroviruses 3:33-39), relatively little regarding the function of the viral protein R (vpr) has been reported. The vpr open reading frame is conserved within all genomes of HIV-1 and HIV-2 and within most, if not all, simian immunodeficiency virus (SIV) genomes. VPR is immunogenic in vivo in that a large subset of HIV.sup.+ individuals makes antibodies that can react with a bacterially produced vpr peptide (Wong-Staal, F., et al., (1987) AIDS Res. Hum. Retroviruses 3:33-39). The most direct evidence for the function of the vpr protein comes from several studies reporting that vpr increases the replication and cytopathogenicity of HIV-1, HIV-2, and SIV in primary CD4.sup.+ T lymphocytes and transformed T cell lines (Ogawa, K., et al., (1989) J. Virol. 63:4110-4114; Shibata, R., et al. (1990a). J. Med. Primatol. 19:217-225; and, Shibata, R., et al. (1990b) J. Virol. 64:742-747), although others have reported vpr has no effect on replication (Dedera, D., et al. (1989) Virol. 63:3205-3208). Interestingly HIV-2 mutated for vpr has been reported unable to infect primary monocyte/macrophages (Hattori, N., et al. (1990) Proc. Natl. Acad. Sci. USA 87:8080-8084). Transactivation of the HIV long terminal repeat and heterologous promoters by HIV is increased about 3-fold in wild-type versus vpr-negative HIV-1, though the mechanism through which vpr may transactivate transcription is unknown and may be indirect (Cohen, E. A., et al., (1990b) J. Acquir. Immune Defic. Syndr. 3:11-18). The relationship between the effects of vpr on promoter activity and viral infectivity is not clear. Vpr protein is incorporated into the viral particle, and this finding has led to the proposition that vpr functions early in infection, following virus penetration and uncoating, and that vpr may interact with cellular regulatory mechanisms important in the establishment of infection (Cohen, E. A., et al. 1990a J. Virol. 64:3097-3099; Yu, X. F., et al. (1990) J. Virol. 64:5688-5693.; and, Yuan, X., et al., (1990) AIDS Res. Hum. Retroviruses 6:1265-1271).